MODE OF SPREAD OF INFECTIVE DISEASES. 751 



the blood and cause the death of the animals which 

 were previously immune (Wyssokowitsch). 



Not uncommonly small injuries due to the most External in- 



. , . . ,, . . fluences ; in* 



various causes seem to prepare the points of invasion j ur i es at the 

 for the reception of the infective agents, and to pave the gjjtsof inva " 

 way for their growth. Experimental proof of this mode 

 of predisposition has been recently brought forward by 

 Orth and Wyssokowitsch ; these investigators were able 

 to set up typical endocarditis in rabbits by first causing 

 trivial lesions of the cardiac valves, and then injecting 

 cultivations of staphylococci ; on the other hand, the 

 infection did not succeed when the cultivation was 

 injected without simultaneous injury of a valve. 



In the intestinal mucous membrane predisposing 

 injuries of this kind may at times be caused by animal 

 parasites, by sharp and pointed constituents of the food, 

 &c. It is possible also that other, though not truly 

 infective, bacteria, which, however, when they multiply 

 to a marked extent in the intestine produce consider- 

 able quantities of ptomaines, and by means of these 

 cause irritation of the intestinal mucous membrane with 

 loosening of the epithelium, may be able to prepare the 

 soil for the true infective agents, and thus give rise to 

 predisposition. 



It is evident that the various factors just mentioned importance of 

 present such manifold though slight differences that the ^ e ^ d oc ^ t * Q 

 different behaviour of individuals and species is very diseases. 

 easily intelligible. It is true that these and especially 

 the individual differences do not play an equally 

 prominent part in the case of all the infective agents ; 

 the more exposed the points of invasion, the more exten- 

 sive and numerous they are, and the more energetically 

 the infective agents in question are able to overcome 

 the resisting power of the cells, so much the less will 

 individual predisposition come into play. These con- slighter in- 

 siderations seem to be especially applicable in the case & ^edis f it {'^ 

 of the acute exanthemata of man, and hence the danger in the acute 

 of infection in these diseases is much more general than c " 

 in other cases where the exciting agents, although they 

 possess the same or even a greater degree of resisting 



