INFECTION. 79 



Another group embraces the so-called essential or malarial fevers, 

 such as febris recurrens, flava, and the Texas cattle-fever ; and, 

 finally, the zoonoses, or contagio-infectious animal diseases, rabies, 

 glanders, anthrax, as well as those peculiar to one species or an- 

 other, as syphilis of man. 



After these general remarks we will now consider what are at 

 present looked upon as the elements of infection, in one form or 

 another, of all these different groups — viz. : 



The Bacteria. 



TThat are bacteria ? 



" Cells deprived of chlorophyl, of globular, oblong, or cylindrical 

 form, sometimes sinuous and twisted, reproducing themselves exclu- 

 sively by transverse division, scissiparity, also by spores, bacillus 

 subtilis, living isolated or in groups, and having affinities to the algae." 



Owing to their microscopic minuteness, it is not to be wondered 

 at that most varying views have been held as to their real nature 

 and place among living things. 



That they constitute veritably a contagium vivum, that is, are 

 living things, there is at present no doubt, various as have been the 

 opinions as to what the true meaning of such a term should be. 



A living contagium is such by which the infectious elements 

 have the principal characteristics of life ; that is, they live and die, 

 and are capable of reproducing themselves : whether the reproduc- 

 tion takes places within or without the animal organism is non- 

 essential to our definition. 



Even very ancient writers seem to have arrived at some vague 

 idea of the existence of a contagium vivum. We find the same in 

 the writings of the Roman fathers of agricultural and veterinary 

 literature of the fourth century, A. D. Varo and Columella, who 

 asserted that many malarial fevers were caused by the penetration 

 of lower organisms into the body. Even before the discovery of 

 the microscope, animal organisms were supposed to have an etio- 

 logical connection with the pest. 



Leeuwenhoek, the father of microscopy, is said to have been the 

 first observer who described anything like true bacteria. This oc- 

 curred in 1675, while examining some water, in which he describes 

 minute globules as crossing the objective field. The following year 

 he recognized similar objects in faeces, and the tartar from the teeth, 

 and gives such descriptions that we are warranted in assuming that 

 they were bacteria, vibrios, and leptothrix. 



An author of the seventeenth century attributed the epizootics 



