ENTRANCE AND SPREAD OF BACTERIA 213 



the ordinary intestinal strain, its virulence having beien 

 heightened by growth in the tissues. 



The micrococcus tetragenus is often found in suppurations in 

 the region of the mouth or in the neck, and also occurs in 

 various lesions of the respiratory tract, in phthisical cavities, 

 abscesses in the lungs, etc. Sometimes it is present alone, and 

 probably has a pyogenic action in the human subject under 

 certain conditions. In other cases it is associated with other 

 organisms. During the war, cases of general infection along 

 with pneumonic symptoms have been recorded in soldiers, the 

 organism having been isolated from the blood ; recovery has 

 been the rule. Cases of pyaemia have been described in which 

 this organism was found in a state of purity in the pus in various 

 situations. In this latter condition the pus has been described 

 as possessing an oily, viscous character, and as being often 

 blood-stained. 



The bacillus pyocyaneus is rarely found alone in pus, though 

 it is not infrequent along with other organisms. We have met 

 with it several times in cases of multiple abscesses, in association 

 with the staphylococcus pyogenes aureus. It is present along 

 with other organisms in a large proportion of old suppurating 

 war wounds. Lately some diseases in children have been 

 described in which the bacillus pyocyaneus has been found 

 throughout the body ; in these cases the chief symptoms have 

 been fever, gastro-intestinal irritation, pustular or petechial 

 eruptions in the skin, and general marasmus. It has also 

 been said to be constantly present in pemphigus, and it 

 certainly occurs in some cases of this disease. It sometimes 

 occurs in cystitis and pyelitis. 



Inflammatory and suppurative conditions, associated with the 

 organisms of special diseases, will Jbe described in the respective 

 chapters. 



Mode of Entrance and Spread. — Many of the organisms 

 described have a wide distribution in nature, and many also 

 are present on the skin and mucous membranes of healthy 

 individuals. The entrance of these organisms into the deeper 

 tissues when a surface lesion occurs can be readily understood. 

 " Their action will, of course, be favoured by any condition of 

 depressed vitality. Though in normal conditions the blood is 

 bacterium-free, we must suppose that from time to time a certain 

 number of such organisms gain entrance to it from trifling lesions 

 of the skin or mucous surfaces, the possibilities of entrance from 

 the latter being especially numerous. In most cases they are 

 killed by the action of the healthy serum or cells of the body, 



