4 IMMUNO-CATALYSIS 



activities of the disease agents. In this connection it may be noted that 

 infections by Sfirochaeta 'pallida, M. tuberculosis, the leprosy bacillus, 

 Actinomycetes and malaria parasites etc., are diseases which habitually 

 run a very slow course and do not show evidence of any fatal toxin 

 which can overwhelm the host before the defenses can be mobilized. 

 Cutaneous and mucous eruptions, inflammatory discharges, the swell- 

 ing of the regional nodes, the malaise, the fever and sensation of chilli- 

 ness, numerous disturbances in the normal physiology of the infected 

 host may likewise be looked upon as the consequences of the inter- 

 action between specific bacterial components and the environment 

 offered by the hosts. 



These considerations bring us to the examination of the possible 

 physiological role of the various constituents of bacteria. Hence the 

 morphological and cultural characteristics, and biochemical activities 

 of bacteria must be studied from the point of view of their relation to 

 infectious diseases, as well as from the view of the biology of the 

 bacterium per se. 



Examining the facts from the standpoint of the biology of bacteria, 

 we see that the enzyme activities of bacteria are indispensable for their 

 growth and reproduction in vitro, as well as in vivo. Invasiveness and 

 fatalness of a bacterial infection are conditioned generally not only by 

 the degree of the resistance offered by the host but, more specifically, 

 by the degree and nature of the enzyme activities of invasive bacteria. 

 The antigenic property of a bacterium, on the other hand, is a conse- 

 quential property; it is conditioned by its propagation in a host for a 

 requisite length of time. This property of bacterial substances would 

 never have come to light if the bacterium had followed an entirely 

 free-living, non-parasitic existence. These facts indicate no doubt that 

 with the exception of highly parasitic forms micro-organisms are not 

 dependent on a host, and, more specifically, not on the antigenic 

 properties of their constituents for existence and propagation. 



On the contrary, the antigenic property is not of utility for the 

 bacterium, but is detrimental to its prolonged propagation within a 

 host. For example, certain infections are followed by effective immu- 

 nity which is instrumental in wiping out the bacteria from the body 

 of a host. On the other, in chronic infections the ineffectiveness of 

 the antigenic property of certain disease agents assures them of a pro- 

 longed existence in a host. 



