GENERAL PHENOMENA OF IMMUNITY 17 



lesions of the surface. Crypt-like structures, such as hair follicles, 

 sweat glands, crypts of the tonsils, gastro-intestinal glands, urethral 

 glands, may serve as foci where bacteria are able to multiply, and 

 may thus determine penetration by the organism. Accessory struc- 

 tures of the skin, such as the hairs of the anterior nares and the 

 cilia of certain parts of the respiratory tract, aid in either filtering 

 the air or in propelling lodged organisms toward external orifices. 

 The nature of certain secretions may be antagonistic to the growth 

 of certain bacteria either by virtue of chemical substances, such as 

 the hydrochloric acid of the gastric juice, normal alkali of the saliva 

 and upper intestinal tract, or by virtue of digestive ferments which 

 may act deleteriously upon bacterial growth. The movement of 

 secretions, as, for example, that of the conjunctival sac, may favor 

 the elimination of organisms. Bodily movement is of considerable 

 value in resistance to infection, whether it be the simple process of 

 wiping away irritating substances or the more intricate process of 

 bathing either with water or with definite anti-bacterial fluids. Re- 

 flexes such as coughing, sneezing, and vomiting are definitely pur- 

 posive in protection. The movement of materials in the intestinal 

 canal serves to prevent any too great bacterial activity, and if in 

 spite of normal intestinal movement irritative substances are formed, 

 the response by diarrhea serves a useful purpose in elimination. 

 Internally the fluids of the body, more particularly the blood, con- 

 tain definite anti-bacterial and anti-infective substances. In addi- 

 tion to these the non-specific ferments of the body fluids aid in 

 combating infection. The acidity or alkalinity of fluids within the 

 body, as well as certain substances of unknown nature, may serve 

 to retard or prevent bacterial invasion. Of great importance in pro- 

 tection is the reaction of inflammation. In the course of this process 

 fluids and cells are exuded from the vessels. The exudation of fluids 

 upon surfaces aids in washing away bacteria, as, for example, the 

 profuse exudation of fluid in acute coryza and acute enteritis. Accu- 

 mulation of fluids may serve to dilute bacterial poisons and by diffu- 

 sion and absorption aid in the elimination of these poisons. The 

 cells which form part of the exudate possess, as characteristic func- 

 tions, the capacity of taking up bacteria by phagocytosis and de- 

 stroying them. The formation of fibrin in the exudate, as well as 

 the subsequent proliferation of fixed tissue cells, serves to delimit 

 the process and thereby aid in the prevention of widespread dis- 

 semination of the organisms. In superficial inflammations the ex- 

 foliation of diseased cells, as in scarlatina, may aid in the elimination 

 of the infective virus. This does not mean, however, that such cells 

 retain an infective character after long periods of desiccation. 



The physiological activity of cells in the body may be so excited 

 as to aid in the elimination of toxic products, as exemplified by the 

 early increase of activity in infectious disease. If the toxic mate- 

 rial be sufficiently virulent this period of hyperactivity may be sue- 



