SCIENCE 



NEW YORK, OCTOBER 21, 1892. 



THE CAUSES OF INFECTIOUS DISEASES. 



BT HUGO ENGEL, A.M., M.D., FELLOW OP THE AMERICAN ACADEMY 

 OP MEDICINE, L. PROFESSOR OF NERVOUS DISEASES AND CLINICAL 

 MEDICINE AT PHILADELPHIA, ETC. 



The real causes producing infectious diseases were unknown 

 until the present era. Preventive treatment, where it existed, 

 was hased upon empirical observations ; and, although the idea of 

 a contagium vivum was conceived a hundred years ago, the possi- 

 bility of a tangible demonstration of the destructive agent under- 

 lying all those zymotic diseases which have so often decimated 

 mankind and wiped whole communities from the face of the earth 

 was scarcely dreamed of a few decades since. 



To-day medicine may truthfully be called thebenefaclrixof the 

 human race ; and, though we are but on the threshold of the new 

 era, yet enough has been already achieved to prove of eminent 

 value to humanity. Only twenty years ago who would have 

 thought it possible that so dreaded an epidemic as the Asiatic 

 cholera could be prevented from entering a country whose borders 

 it had reached, and that the fatal malady when it had once found 

 victims in a populous city could be limited to the imported cases 

 attacked, and its further progress be halted? Here we had 

 cholera at our very doors ; but it could not enter, and a whole 

 continent has escaped its deadly visit. '"• In such great centres of 

 human industry as New York and Berlin, where thousands of 

 strangers daily arrive and depart, a few cases occurred, but the 

 ghastly disease was driven off without its being able to select one 

 more victim ! 



Such facts prove the value of the achievements of modern medi- 

 cine, and clearly show the immense progress this science has made. 

 The question naturally occurs to the intelligent mind — how was 

 it possible to achieve what but recently has seemed unattainable? 

 And the answer is — because of the knowledge gained by bacteri- 

 ology, this new but all-important branch of modern pathology ! 



Let us glance at the recent discoveries and bring before our 

 mental eye the principles underlying the study of infectious dis- 

 eases. At the boundary of the animal and vegetable kingdoms 

 there is an immense empire of beings so minute that the naked 

 eye cannot see them, and that the most powerful microscope alone 

 does not suffice to determine the various species. So difiBcult be- 

 comes here the recognition of the individual that for years the 

 most eminent authorities were in doubt how to classify these 

 minute organisms. Are they animals or plants ? The weight of 

 testimony has at last decided in favor of the empire of plants. To 

 it belong these micro-organisms, of which millions weigh but one 

 grain, but which have the power of multiplying at such an ex- 

 traordinary degree that, as Cohnheim has calculated, the breed of 

 bacteria springing from one germ about ^-j^ of a millimeter in 

 length and j^Vsr of a millimeter in thickness, provided the devel- 

 opment and multiplication could go on without hindrance, within 

 less than five days would completely till all the oceans of the earth, 

 and the descendants of one single micrococcus, whose weight is 

 so little that sixteen hundred millions of them weigh but one 

 grain, would within three days reach the enormous weight of 

 fifteen million pounds ! But fortunately natm-e has placed im- 

 pediments in their way ; they can develop only under certain 

 favorable conditions, otherwise how soon would these diminutive 

 little beings overpower every living organism ! 



There are two great subdivisions of these microbes, hyphomy- 

 ceti and schizomyceti. The first, so-called moulds or fungi, mul- 

 tiplying mainly by the aid of spores, are parasites, among which 

 are many that give rise to diseases of the skin and mucous mem 



brane, as favus, thrush, etc. The propagation of the second class 

 — schizomyceti — takes place mainly by division. Most of them 

 have a rod-like form. The Greek word for rod is paK-r/piov ; hence 

 the term bacterium. But not all have the same shape, and ac- 

 cording to their forms they are arranged in six classes: — 



1. Micrococci, or cocci, with circular shape. 



3. Bacilli, including all rod-shaped bacteria, short or long. 



3. Bacteria proper, as which science recognizes only the shortest 

 bacilli. 



4. Vibriones, rods of wavy shape. 



5. Spirilli, forming short, stiff screws. 



6. Spirochaeti, having the form of long, flexible screws. 

 Modern research with positive certainty has demonstrated the 



fact that the activity of bacteria is not limited to the production 

 of one kind of processes. While many of them never prey upon 

 the human organism, others are pathogenic, i.e., disease produc- 

 ing; but the first condition necessary to their development is their 

 entrance into the living human or animal body. One class of 

 schizomyceti, the so-called septic bacteria, at once begin their 

 enormous propagation, when death has interrupted the mechanism 

 of life and the organized tissue having ceased all motion is decom- 

 posed, decays, ferments, and putrefies. To-day it is a recognized 

 fact, undisputed by any authority, that the process of putrefaction 

 by which the dead organized tissue returns its constituent parts to 

 the inorganic world and thus completes the never-ending circle, 

 is caused by the septic microbes alone. Without them there can 

 be no decay. All our disinfectants, our processes of embalming, 

 our methods of preserving organic substances by complete exclu- 

 sion of air, are based upon one principle — preventing the develop- 

 ment of septic bacteria. 



Another kind of these minute organisms gives rise to various 

 chemical changes known as fermentations. The process by which 

 sugar is changed to alcohol and carbonic acid is due to the yeast- 

 plant; when fermented fluids become acid, this c'lange to the 

 vinegar fermentation is caused by another bacterium; that milk 

 turns sour a rod shaped schizomycete is responsible for; the dis- 

 colorations noticed on potatoes, cheese, boiled eggs, etc., as well 

 as the blueish and yellowish tint sometimes assumed by milk, and 

 the green and blue color of pus, are produced by bacteria. The 

 remarkable incident which has caused so much religious supersti- 

 tion, viz., that on the holy wafer appeared a drop of blood, 

 simply depends upon decomposition induced by a micrococcus 

 (Monades prodigiosce, Ehrenberg), and is met with also in un- 

 leavened bread. 



But bacteria do not cause only the decomposition of dead or- 

 ganic substances, they extend their fiendish power also to the 

 destruction of the processes of life of the highest organized beings 

 — the human race and the animals nearest to it. 



It would lead me here too far to narrate how the discovery was 

 made, and how by patient research and logical reasoning science 

 has at last succeeded in determining the true cause of infectious 

 disease. Suffice it to say that every zymotic malady — be it 

 acute, like cholera, pneumonia, typhoid fever, small-pox, chWken- 

 pox, scarlet-fever, measles, whooping-cough, yellow-fever, inter- 

 mittent or remittent fever, cerebro;spinal fever, erysipelas, diph- 

 theria, etc., or chronic, like tubercular consumption, cancer, 

 chronic malaria, lupus, etc. — is due to some special micro- 

 organism, which during the process of development and multipli- 

 cation in the human (animal) tissues gives rise to the formation 

 of ptomaines, — highly organized and most virulent poisons, — 

 which in their turn produce the phenomena, the group of symp- 

 toms, that characterize an infectious disease. And the more active 

 this process of development, the greater the number of the bac- 

 teria introduced into the living organism, the more favorable the 

 soil presented to them, the more viru ent is the ptomaine, the 



