80 THE BACTERICIDAL SUBSTANCES OF THE BLOOD 



f erence of the leukocytes to ordinary conditions again led to an active 

 production of "leukins," the cells having apparently not been 

 damaged by their exposure to the carbon dioxide. Corresponding 

 results were obtained with Bier's congestive lymph, and satisfactory 

 proof thus furnished that these bodies are formed in vivo as well as 

 in vitro. Schneider, hence, naturally concludes that the beneficial 

 effect obtained with this method of treatment is probably due to 

 the increased production of these substances. 



What the determining factor is that causes the secretion of leukins 

 is unknown, but we may well imagine that a special stimulus may here 

 be operative, and that such substances may be liberated from the 

 tissues at large under various conditions which need not necessarily 

 be pathological. 



While the above-mentioned bactericidal substances, namely, the 

 bacteriolysins of the serum and the leukins or endolysins of the leuko- 

 cytes, unquestionably exist as such in the plasma, another substance 

 or group of substances which may likewise be viewed as protective 

 agents or alexins, in the wider sense of the word, are formed only 

 during the process of coagulation from the blood platelets, as has 

 been satisfactorily demonstrated by Gruber and Futaki. Their 

 action, however, seems to be directed almost exclusively against 

 the anthrax bacillus and its congeners. 



Summary. To sum up then: we have become acquainted with 

 various defensive agents on the part of the animal body, any one or all 

 of which may become operative after infection has once occurred, 

 i. e., after a given organism has penetrated through the external 

 epithelial barriers of the body; and knowing some of the offensive 

 weapons of the invaders, we can form a conception of the manner in 

 which systemic invasion may take place or in which it may be pre- 

 vented. A great deal will, of course, depend upon the quantitative 

 relations existing between the offensive and defensive factors which 

 are engaged in the strife. 



Offensive-defensive Mechanism in Infections with Necroparasites. 

 If the invader is actually open to attack at the point of infection by 

 those agents which are at the disposal of the host, a successful resist- 

 ance is at least possible, which may carry with it the recovery of the 

 infected individual. This, however, is not necessarily the case. For 

 we have seen already that some organisms, such as the tetanus 

 bacillus, are capable of producing poisons of such potency that 



