592 MICROBIOLOGY OF THE DISEASES OF MAN AND ANIMALS. 



due to a thermolabile ferment-like substance known as gelatinase. In milk, the 

 staphylococcus grows readily and causes coagulation sometimes early but usually in 

 three or four days' time. On potato growth is usually abundant; it is not as moist nor 

 as smooth as on agar and is slower. Pigment is developed usually to the highest 

 degree and sometimes cultures appearing white on agar develop pigment on 

 potato. On inspissated blood serum growth is usually moist and abundant. Occa- 

 sionally the growth sinks slightly into the medium suggesting partial liquefaction. 

 In dextrose, lactose and saccharose media acid is produced, but no gas. Acid is a con- 

 stant product. Formic, lactic, butyric and valerianic acids have been found and 

 probably other fatty acids occur. Some authorities state that indol is formed but 

 negative results are the rule. Nitrites are formed by the reduction of nitrates. 

 A characteristic odor from cultures is due probably to the presence of fatty acids. 

 The pigment appears in aerobic cultures and is absent in anaerobic cultures. It is 

 insoluble in water but soluble in alcohol, chloroform, ether and benzol. The toxins 

 are largely intracellular. A thermolabile, haemolytic substance may be found in the 

 more virulent strains after about ten days' growth in moderately alkaline broth and can 

 be freed by nitration through procelain filters. Another soluble toxic substance is 

 found, causing the death of leucocytes leucocidin. It is considerably less stable than 

 the staphylo-hcemolysin. The staphylococci are among the most resistant of the non- 

 spore bearing bacteria. Sometimes 60 for a full hour or even longer is necessary to 

 kill watery suspensions; 70 is usually necessary to kill in ten minutes. If organic 

 material is present the resistance is of course much greater. Low temperatures have 

 little effect and it has been stated that 30 per cent have survived thirty minutes' 

 exposure to liquid air. To direct sunlight and drying staphylococci also show consid- 

 erable resistance and may be found in dried pus for several months. Resistance to 

 germicides is also somewhat greater than that of other vegetative bacteria, and 

 is increased especially in the presence of organic material. In watery suspensions 

 staphylococci are killed by 1:1000 mercuric chloride in ten to fifteen minutes, by 3 per 

 cent carbolic acid in two to ten minutes and by 5 per cent formaldehyde in the same time. 



Man seems to be considerably more susceptible to staphylococcic in- 

 fections than animals. Of the latter rabbits and mice and guinea-pigs are 

 susceptible in this order. 



The virulence of the organism shows considerable variation and is 

 usually increased by successive passages through animals of the same 

 species while remaining unaltered for animals of other species. 



Subcutaneous inoculation usually results in abscess formation. 

 Virulent cultures injected into the peritoneal cavity of animals may kill 

 in forty-eight hours to a week or even longer with pyaemic abscesses 

 especially in the kidneys. Malignant or ulcerative endocarditis has 

 been experimentally produced by intravenous injection when the heart 

 valves have been injured, chemically or mechanically. Osteomyelitis has 

 also been experimentally produced. 



