the various methods of performing vaccination, or even to describe the course of true vaccinia, important as these topics are, but must hasten to discuss very imperfectly a few of what I conceive to be the more interesting and attractive questions connected with this subject. The introduction and extensive progress of animal vaccination in this and other countries within the last few years, very naturally suggests the question, both to the profession and the public, what is the comparative value of bovine and humanized vaccine virus? I have studied this question very carefully, and have no hesitation in saying that there is really no difference between the action of bovine virus and that of recent humanization; but between the action of either of either of these viruses and that of long humanization, there is a very marked difference. Vaccinia induced by animal or recently humanized virus requires for the fullest development and completion of its course not less than twenty-one, and frequently as long as twenty-eight days-counting from the time of insertion of the lymph until the falling off of the crust-and is sure to be followed by an indelible scar, distinct and well-defined as if stamped by a sharply-cut die. On the other hand, vaccine virus far removed from its original source induces a vaccine disease of much less intensity and of considerably shorter duration. The scar also differs in a corresponding degree, being much less distinct and often quite uncharacteristic.

In 1836, when the cow-pox of Passy was discovered, there was found to be a very great difference between the course and duration of vaccinia, resulting from the use of the new virus, and that of the old; the latter at that time represented thirty-eight years of uninterrupted human transmissions. In 1844, after eight years of humanization of the Passy stock of virus, it produced vesicles which ran their full course in three days less time than when it was first discovered. The vesicles of the Jennerian stock of virus, after thirty-nine years of uninterrupted human transmissions, were found to undergo desiccation in twelve days, instead of seventeen, which is the standard period, losing in that time five days of their maturing period. The late Dr. Martin, in one of his very valuable contributions writes that, in 1859, he obtained from Ceely a supply of long-humanized lymph which he continued to propagate for several years, and that the course of the disease induced by this virus was usually eleven days, counting from the time of insertion until the crust would fall off, or could be readily removed. He also says that for nearly ten years he propagated virus which he received from the National Vaccine Institution of Great Britain, and that this virus induced a disease, the duration of which was fourteen days, very exactly, from insertion till the fall of the crust. When a public vaccinator in this city, from 1867 to 1870, which was prior to the introduction of animal vaccination in this country, and the stock of virus in use doubtless being the same as that from the National Vaccine Institution of Great Britain, I found it necessary,

in order to collect crusts for further use, to visit the persons I vaccinated not later than the fourteenth or fifteenth day after inserting the virus; if I delayed my yisits to a later day my harvest of crusts would prove very scanty. How different is all this from our experience at the present time! The virus now in general use is either bovine or not many removes from the animal, and I am sure we will all agree that, in the vaccinations of to day, it is impossible to remove the crust, without doing violence to the arm, earlier than the end of three weeks, and frequently not until the end of the fourth.

My experience leads me to assert most positively that vaccinia of short duration is capable of destroying in a person the susceptibility to small pox. But whether the protection it asserts is as durable as that which results from the more typical form of the disease, I have good reason to doubt. On account of the greater reliability and certainty of action and more speedy action of humanized virus somewhat remotely removed from the heifer, I very much prefer it to bovine for vaccination after exposure to the small-pox contagion. Over and over again have I been able to give absolute protection against small pox by the use of long-humanized virus employed after there was undoubted and continuous exposure. Bovine lymph employed under such circumstances has not given me anything like the same satisfactory results; and for no other reason than its uncertainty and slowness of action.

As already intimated, it is my opinion that the prophylactic power exerted by long-humanized virus is less durable than that exerted by bovine lymph or lymph of recent humanization. This opinion is not based on any direct proof, but rather on a strong inference or logical deduction which cannot be elaborated in the brief time assigned me. During the last several years there has been a growing belief in the popular mind that humanized virus is liable to convey into the system some constitutional taint. Whether this fear is real or imaginary, I will not stop to consider; but surely animal virus is free from any such imputation, and therefore its introduction into general use is calculated to minimize the opposition to vaccination. Another advantage possessed by animal lymph is that in time of a wide-spread epidemic of small-pox, virus sufficient to vaccinate whole communities can be furnished at short notice.

The question is often asked, are multiple vesicles more protective than single ones? Most writers, I know, answer this question in the affirmative, but my own experience leads me to say that a single, typical vesicle, running regularly through its various stages, gives as great protection as it is possible to obtain from a dozen or more. If, however, the virus to be used is of long-humanization and quite weak in its action, it would be well to make three or four insertions. The practice of making multiple insertions doubtless grew into use in consequence of the deterioration of long-humanized virus.

I will not waste time by proving to you what is so well known, namely, that vaccination exerts a prophylactic power against smallpox. I will briefly dispose of this question by saying that the occurrence of small-pox, in any form, after a recent, typical vaccination, is very rare indeed; and even in the rare instances in which varioloid does occur, the attack is so mild that death never results except, perhaps, in a very feeble person.

While vaccination almost always confers perfect protection against small-pox, that protection, particularly if it be conferred in infancy, cannot be depended upon to continue throughout the life-time of the individual. If, however, the vaccination be done later in life, say at ten, twelve or fifteen years of age, the chances of the protection being permanent are much greater. It seems probable, therefore, that the changes in the system incident to puberty have in some unknown way much to do in reëstablishing the susceptibility. I do not wish to be understood as saying that protection from vaccination in infancy is never permanent, for that cannot be truly said. Perhaps in about 25 per cent. of persons there is not the least deterioration of the protection by time; but in the other 75 per cent. various degrees of susceptibility are reëstablished in the course of a variable length of timesome taking small-pox in a very mild form, and others as severely as if vaccination had never been performed. The character of the vaccine cicatrix even cannot be depended upon as clearly determining anything in regard to susceptibility. It is true that a good cicatrix is stronger evidence of protection than a poor one; but it must be remembered that it is only evidence, not proof. I have seen hundreds of persons who were vaccinated in infancy and presenting typical cicatrices suffer from small pox in adolescence and adult life; and the death-rate among this class of patients is far from being insignificant. The sooner, therefore, the public, and, I may say, the profession too, come to recognize the fact that vaccination in early life, however typical, cannot be depended upon to confer permanent immunity from small-pox, the sooner will communities be spared from the decimating effect of constantly recurring epidemics of this most horrible disease, because such a knowledge would lead to the more general adoption of re-vaccination.

This brings us to consider, lastly, the value of re-vaccination. Many think that because the vesicle of re-vaccination does not as a rule pursue the regular course of that of true vaccinia, the effect is merely local, exerting no prophylactic power whatever, and therefore that re-vaccination is unnecessary. . But surely re-vaccination, to be successful, need not necessarily pursue the typical course of vaccine, for we know that small-pox itself after vaccination frequently differs very markedly from the course of the true disease. If then we have modified small-pox, or varioloid; after vaccination, may we not also have modified vaccinia, or vaccinoid? Believing this, as I do, the conclu

sion is inevitable that as varioloid gives protection against a recurrence of small-pox, so also does vaccination exhaust whatever susceptibility to the disease may have been acquired since the previous vaccination.

At what age should re-vaccination be performed? The answer to this question depends very much upon the thoroughness of the primary vaccination. A child well vaccinated in infancy only occasionally takes re-vaccination under ten years of age; but under circumstances of great exposure to the contagion of small-pox, it would be well to re-vaccinate children somewhat under that age. During the second decennial period of life the necessity for re-vaccination very greatly increases. A person who has been well vaccinated in infancy, and again at or above the age of fifteen years, will, as a rule, remain protected for the remainder of life. But if one wishes to feel perfectly sure about his protection, it would be well to have re-vaccination done whenever small-pox prevails.

In seeking for evidence to prove the efficacy of re-vaccination, we need only consult the statistics collected during the Franco-Prussian war. It is well known that in no country is vaccination more carefully and systematically performed than in Germany. Every infant there is vaccinated before it has completed its first year, and re-vaccination is done at or about the twelfth year. Every person entering the army is again vaccinated, and, if that fails, the operation is repeated until the surgeon is satisfied that the person is insusceptible to vaccinia. Hence the Germany army may be said to be a well vaccinated army. On the other hand, in the French army vaccination and re-vaccination were in no wise compulsory. During the war small-pox prevailed to an alarming extent, and both armies were freely exposed to the contagion. The loss by death from that disease in the German army was only 263 men, while the deaths in the French army amounted to the enormous proportion of 23,468; and the French army was never very much more than one-half the size of the former. Physicians connected with hospitals for the treatment of small-pox bear testimony very uniformly to the fact that persons with a history of successful vaccination and re-vaccination are very rarely admitted. as patients. Not only is this true in my own experience, but, furthermore, I have never seen a nurse, or any employé in the hospital in this city take small-pox, provided vaccination or re-vaccination was well performed before entering upon duty. While, on the other hand, the disease has attacked a few such attendants, in whom re-vaccination was for some reason omitted or neglected.

Did time permit I might add very largely to the evidence presented in this paper proving the prophylactic power of vaccination; but we have before us, I think, facts sufficient to warrant the conclusion that if vaccination were effectively performed in infancy, and re-vaccination universally employed at the age of puberty, the world would then

begin to realize that Jenner was no mere dreamer when he claimed for vaccination the power to extirpate small-pox from the face of the earth.

XXI. The Present and Prospective Sanitary Condition of Pittsburgh, Pa.

By CROSBY GRAY, Health Officer of Pittsburgh.

For convenience of description and simplification of details, we deem it advisable to divide the city into three divisions. Nature did this for us originally, while the site was still an unbroken wilderness, but instead of three divisions she made four. On one of these, viz: that portion lying north of the Allegheny river, is located the city of Allegheny, with a population of 95,000. It is connected with Pittsburgh by numerous bridges, and although practically forming a part of it, it has a separate municipal government and does not come within our jurisdiction. There remain then to the city the three natural divisions locally known as the "Old City," the "East End" and the "Southside," containing an area of 29.3 square miles, and a population of 200,000. In general terms the population clustered around the point where the Allegheny and Monongahela rivers unite to form the Ohio may be modestly estimated in round numbers at 300,000.

"OLD CITY."

The portion known as the Old City comprises the original twelve wards, and is located in the angle formed by the union of the Alleggheny and Monongahela rivers, extending back to a line of hills, rising at its highest point 530 feet above the level of the rivers, and which formed originally a natural barrier to the extension of the city into what we now term the "East End" division.

The old city contains an area 2.1 square miles and a population of 70,000. Its topography is very irregular, there being little or no level or marshy ground.

It is admirably located for drainage. Perhaps it was on account of these natural advantages that during many years of its history no systematic plan of sewerage was devised and constructed to meet the requirements of its increasing population. A rigid economy seems to have been exercised in this direction for the reason, perhaps, that its topography necessitated the expenditure of large sums for grading its streets, heavy cutting and filling being required to a much greater extent perhaps than in any other city in the country.

The sewers have almost all been constructed within the last 25 years, having been gradually extended as the property became sufficiently valuable to pay the assessments levied for their construction.