46 MEDICAL MYCOLOGY 



superficial lesions but causes unpleasant discolorations and in some individuals 

 severe poisoning. It is rarely used about the laboratory as a disinfectant. 

 The alcoholic solution is occasionally used as a counterirritant. 



Salts of Heavy Metals. — In general, salts of heavy metals are toxic to or- 

 ganisms roughly in the order of the magnitude of their atomic weights, al- 

 though the salt radical has some less clearly defined influence on toxicity. 

 Copper compounds are frequently used in agricultural practice as a fungicide 

 but rarely about the laboratory. Compounds of mercury have had great 

 vogue, especially in some laboratories, but they have some severe drawbacks 

 and probably many may be well replaced by other disinfectants. The oldest 

 and most widely used is mercuric chloride (bichloride of mercury, corrosive 

 sublimate). Toxic in extreme dilution, the solution is apt to dry, leaving tiny 

 crystals which blow about the laboratory and occasionally prevent growth 

 when all other conditions are favorable. Glassware which has been used for 

 mercuric chloride solutions should never be used for cultures again, for if 

 growth takes place at all, it is apt to be abnormal and stunted. In some per- 

 sons it also causes severe dermatoses extending over several years. The 

 recently developed mercurochrome has eliminated several of these objections. 



Silver nitrate (lunar caustic) has long been in use and recently some of 

 the organic silver salts, especially nucleinates (argyrol and similar com- 

 pounds) have been widely used about the mouth, ej'es, and genitalia. 



Organic Compounds. — Of the innumerable organic compounds only the 

 lower aliphatic alcohols and aldehydes and the simpler compounds of the 

 aromatic series, such as phenols and salicylic compounds, have found wide 

 use. Methyl alcohol is quite efficient, but is rarely employed on account of 

 the injury of the optic nerve by the vapors. Ethyl alcohol is perhaps the most 

 widely used of the group. Absolute ethyl alcohol has little value, but the 

 intermediate dilutions with water are good, especially for sterilizing cutting 

 instruments which cannot be subjected to heat or to the stronger, but more 

 corrosive, disinfectants. The higher alcohols are little used. 



Formaldehyde had a great vogue at one time as a gaseous disinfectant, 

 but now is seldom used about the laboratory, except in aqueous solution 

 (formalin) in seed disinfection and as a cheap preservative for class material. 



Phenol (often knoAvn in its 4% aqueous solution as carbolic acid) has 

 stood the test of half a century, although its popularity has varied. For many 

 years it was taken as a standard for comparison of the efficiency of antiseptics. 



Salicylic compounds belong rather to medicine, although salicylic acid 

 itself is used externally in dermatology as a keratolytic agent. 



Volatile oils have been found useful with pathogens of the skin (Kingery 

 et al. 1928, 1929). 



Physical Ag-ents. — Heat and light are the only sterilizing agents in gen- 

 eral use at present, although it is probable that radiations of still shorter wave 

 lengths would be effective if not so expensive. Light, especially the ultra- 



