140 THE DISEASES AND DISOEDEES OF THE OX. 



possess the power of growing and thriving in the bodies of cer- 

 tain suitable animals, in them producing a definite pathological 

 condition. 



" Just as there are species of plants which act as poisons to the animal body, 

 and other species of plants which, although belonging to the same group and 

 family, and although very much alike to the others, have no such power, and 

 cannot acquire such power by any means, so there are micro-organisms which 

 are pathogenic while others are harmless. " — Klein. 



The latter remain harmless, no matter under what conditions 

 and for how long a time they grow. Further, it is most pro- 

 bable that careful and thorough drainage and the removal of all 

 tendencies to wet and putrefaction must gradually bring about 

 a gradual diminution of plagues, at least, such as are similar in 

 their nature to anthrax. Other diseases also, such as ague and 

 other malarial fevers, are occasioned by the prevalence of germ- 

 containing vapours arising from ill-drained marshy lands on 

 which the vegetation is always liable to undergo putrefactive 

 change. Having briefly alluded to the germ-theory of disease, 

 and having attempted to indicate the kind of way in which some 

 diseases may have first originated, we now proceed to discuss 

 other aspects of our present subject. 



When dealing with the phenomena displayed by higher 

 animals, we must remember that they, the animals, may all be 

 considered as being composed of innumerable cells, or struc- 

 tures more or less closely resembling cells. A cell is a minute 

 and generally microscopic body consisting of living matter 

 called protoplasm or bioplasm, and containing in its interior an 

 independent rounded body, also living, and called a nucleus. 

 These cells have been modified in all kinds of ways and degrees, 

 in correspondence with, and, so to say, in order to meet the 

 many diflfereut requirements of more complex conditions. True, 

 we cannot entirely explain the ways in which such effects are 

 brought about, but we can very appreciably lessen the difficul- 

 ties which most gravely impress us. The higher and more 

 perfect an organism is, the more intimate is the combination of 

 the many parts of which it is made up. These parts are united 

 in various ways, and when thus united they are, moreover, still 

 more wonderfully blended by connecting links of different kinds. 

 Hence it comes about that in our attempts to explain the pro- 

 cesses of life, whether normal or abnormal, we must bear in 



