528 MICRO-ORGANISMS AND DISEASE [chap. 



extent various bacteria — the bacillus anthracis, cholera 

 spirilla, the typhoid bacillus, micrococcus tetragenus, and 

 staphylococcus aureus gradually die off when kept in 

 ordinary drinking water, i.e., water very poor in nutritive 

 materials. (The results of Meade Bolton are published 

 in the Zeitschrift fiir Hygiene, i. i, p. 76; those of Wolff- 

 hiigel and Riedel in the Mittheil. aus dem k. Gesundheitsamte, 

 Berlin, i. p. 455. See also G. and P. Frankland's Handbook 

 on Water Examination^ 



It need hardly be said that if even small amounts of 

 nutritive material be added to water these bacteria will 

 have a better chance of survival and of multiplication, and 

 this chance will be proportionate to the amount of nutritive 

 material added. Similarly De Giaxa (Zeitschrift f. Hygiene, 

 vi. 2, p. 162) made observations with reference to the con- 

 ditions of existence of various bacteria in sea water, and his 

 results are parallel to those made on ordinary drinking 

 water. It need not be specially insisted on that neither 

 ordinary nor sea water in themselves have any killing power 

 on bacteria, but that where such an inhibitory power is 

 observed it is due to the want of sufficient nutritive material, 

 and that the greater the dependence of bacteria on organic 

 material, and the poorer the water in such material, the 

 more unfavourable is such water for the existence and 

 multiplication of those bacterial species. 



Next we have to consider the relations between two or 

 more species simultaneously present in the same medium 

 with sufficient nutritive material. Here more rapid multi- 

 plication will naturally depend, ctzteris paribus, on the 

 greater assimilative power ; the greater this is, the more 

 predominating will the species become. Thus, for instance, 

 if in any organic material, say dead animal tissues, saprophytic 

 bacteria are present together with bacillus anthracis, this 



