MICROBIAL DISEASES OF MAN AND DOMESTIC ANIMALS 793 



facultative anaerobe. It grows readily on all routine media, preferring a reaction 

 slightly alkaline to litmus. Growth on plain agar is rapid and abundant. After 

 twenty-four hours there appear round grayish-white or yellowish colonies about 2 

 mm. in diameter, smooth and raised above the surface of the medium. Micro- 

 scopically, the colonies are regular in outline and finely granular. The char- 

 acteristic orange-yellow pigment may not appear until later or if already present in 

 twenty-four hours, deepens with further growth. In broth, growth is also rapid 

 and causes a diffuse clouding with a thin pellicle and a heavy sediment after several 

 days. In gelatin, colonies are as on agar and sink into cup-like depressions as the 

 medium is liquefied. Liquefaction is rapid with some strains and slower with others, 

 and in old cultures is of a funnel or saccate type. It is 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. Occasionally 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 constant 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 filtration through porcelain 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 tem- 

 peratures 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 considerable 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 i : 1000 mercuric chloride in ten to fifteen 

 minutes, by 3 per cent carbolic acid in two to ten minutes and by 5 per cent formal- 

 dehyde 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. 



