THE IDEAL DISINFECTANT 187 



Cold. Cold has practically no effect upon bacteria and their 

 spores; alternately freezing at very low temperatures and subsequent 

 thawing, however, destroys the vegetative form of some pathogenic 

 bacteria. Cold has, accordingly, no place in the armamentarium of 

 practical disinfection. 



Direct Sunlight. The chemically active blue, violet, and ultra- 

 violet rays of the spectrum have a particularly strong germicidal effect 

 upon both the vegetative forms and spores. The effect, however, is 

 limited to the surface of objects. The beneficial effect of sunlight 

 should not be underestimated, particularly in veterinary practice, 

 where the great majority has not yet learned the importance of having 

 stables, barns, and other places where animals are kept well lighted 

 during the day and particularly well lighted and exposed to the sun 

 after the prevalence of infectious diseases. Arloing noted the effect 

 of sunlight upon anthrax bacilli and spores. Pansini showed that the 

 bacilli in cultures are killed in from one to two and one-half hours; 

 the moist spore directly exposed in one-half to two hours; the dried 

 spores in from six to eight hours. Koch and others demonstrated 

 the germicidal effect of sunlight upon tubercle bacilli. Rosenau 

 found that the plague bacillus exposed to the direct action of the sun- 

 light dies in half an hour, provided that the temperature is above 30 C. 

 Even diffuse daylight, when acting long enough, has an inhibiting 

 and detrimental effect upon many pathogenic bacteria, but it is very 

 much slower than the effect of direct insolation. 



Drying. Some bacteria, like the glanders bacillus, the cholera 

 spirillum, etc., are very rapidly killed by drying out, while others, like 

 the tubercle bacillus, are only affected after they have been dried out 

 for a long time. Certain spores, like those of anthrax, remain alive 

 and virulent even after many years. 



Electric Currents, X-rays, and Radium. Electric currents, accord- 

 ing to Zeit and others, have no direct effect upon bacteria, unless 

 they are in solutions which give rise to detrimental electrolytic prod- 

 ucts, such as acids, ozone, etc. The arrays, according to the same 

 author, appear to have no germicidal effect. Radium emanations 

 have an appreciable effect; they have killed anthrax spores after an 

 exposure of three days. This effect, however, seems to depend entirely 

 upon the easily absorbable rays and not upon the deeply penetrating 

 rays, and is, therefore, only superficial. 



The "Ideal" Disinfectant. An ideal disinfectant would be one 

 which, while highly efficient, deeply penetrating, and absolutely trust- 

 worthy, would not damage any of the objects to be disinfected. Such 

 a disinfectant does not exist. Moist heat is excellent for cotton, wool, 

 and linen, but it destroys leather, harness, etc. Formalin is strong 

 and effective, does not easily damage, but its penetrating power is 

 deficient. Some of the most important disinfectants extensively used 

 in practical every-day work are the following: 



