148 A MANUAL OF BACTERIOLOGY 



along with the bacteria, a large quantity of their 

 products (ptomaines) are introduced, these products 

 interfere with the action of the cells, and enable the 

 bacteria to get a foothold. If a large number of 

 bacteria are introduced at one place they grow for a 

 time till attacked by the cells, and each produces a 

 small quantity of poisonous material. Where the 

 number of bacteria is very large this material 

 destroys the tissues in the neighbourhood, and 

 enables the bacteria to spread over a large area 

 before the layer of cells formed around them is able 

 to form a barrier against their progress. The extent 

 to which they spread in other words, the size of 

 the abscess which results must, therefore, depend 

 firstly on the number of bacteria and the quantity 

 of products introduced in the first instance ; and, 

 secondly, on the vitality of the animal. It may be 

 that a very large amount of organisms is introduced 

 in the first instance, producing such an amount of 

 poison as to kill the animal in a few hours.' The 

 investigations of Watson Cheyne, as well as those of 

 Hauser, undoubtedly prove that a ptomaine of 

 poisonous properties is formed by these bacteria 

 (Proteus vulgaris), but there can be no doubt, also, 

 that these bacteria themselves are truly pathogenic 

 for rabbits under proper conditions. Watson Cheyne 

 has also shown that when Proteus vulgaris is grown 

 in bouillon it acts with less virulence than when it 

 is grown in nutrient gelatine. 



Proteus mirabilis. This bacterium is something 

 like the preceding microbe, although somewhat 

 shorter. It liquefies gelatine much slower than 



