750 MODE OF SPREAD OF INFECTIVE DISEASES. 



especially in the epithelium, which, although scarcely 

 noticeable, have nevertheless a marked effect, and permit 

 or prevent the growth of the infective agents. Loeffler, 

 in his investigations on diphtheria, has brought forward 

 a very beautiful experimental proof of the importance of 

 the character of the epithelium ; he showed that young 

 guinea-pigs could be infected in the vagina by cultivations 

 of the bacilli of diphtheria, evidently because the epi- 

 thelium of the mucous membrane is extremely delicate 

 and easily injured ; older animals, whose vagina is pro- 

 tected by tough epithelium, were, on the contrary, quite 

 insusceptible to this mode of inoculation. The variation 

 in predisposition in accordance with age which is seen 

 in various human infective diseases, must probably be 

 in part referred to a similar influence of the epithelium 

 at the point of invasion. Further, many facts point to 

 the view that even the very slightest pathological altera- 

 tions or loosening of the epithelium, such as usually 

 occurs in catarrhs for example, also render infection 

 easier. 



influence of Further, the condition of the other more deeply 

 the other cells. p] ace( j ce ]} s o f the affected organ is also of importance 

 for the occurrence of the disease. The endothelial cells 

 of the capillaries, and to a very marked extent in some 

 organs the cells of the lymphoid tissue, appear to play 

 an important part in the battle with the attacking 

 bacteria, and on the vital energy of these cells the result 

 of the battle its rapid termination before general infec- 

 tion occurs, or its continuation in ever-increasing dimen- 

 sions will depend to a very marked degree. In the 

 case of the endothelial cells of the blood vessels it can 

 be experimentally shown how a general depression of 

 the cell energy by poisons, and especially by ptomaines, 

 leads to a totally different ending to the battle in which 

 in the normal condition these cells are, in the case of 

 certain species of bacteria, always victorious ; it can be 

 shown that, under the influence of ptomaine poisoning, 

 the same bacteria which formerly quickly died in the 

 endothelial cells, and never caused disease in the 

 animals, are now able to multiply extremely rapidly in 



