278 STERILIZATION, ANTISEPSIS AND DISINFECTION 
microorganisms; in effective concentrations they appear to form com- 
binations with tissues if they are used in or on man. 
Immune Sera as Disinfectants.— Disinfection of the tissues has 
been attempted with specific bactericidal sera, which are without 
noteworthy harmful effects upon the patient. At the present time 
immune sera are not wholly satisfactory for this purpose, but suffi- 
ciently encouraging results have been obtained to justify their present 
use and to afford promise of their improvement in the future. 
A majority of chemical disinfectants are, to use Ehrlich's termi- 
nology, organotrophic rather than parasitotrophic, that is, they have 
a greater affinity for the tissues of the host than for the parasite. 
Quinine, on the contrary, appears to be parasitotrophic— it is almost 
a specific for malarial parasites. Ehrlich's brilliant researches in 
chemotherapy have added organic compounds containing arsenic to 
the list of parasitotrophic substances; they have a very direct and 
inimical action upon trypanosomes and the Treponemata, and but 
minimal action upon the tissues of the host. 
Formaldehyde.— A solution of formaldehyde gas in water, commer- 
cially known as formalin, is a powerful disinfectant; it does not react 
as strongly as mercuric chloride with protein solutions;^ it does not 
injure metals or ordinary fabrics. The commercial solution contains 
about 35 per cent of formaldehyde, hence a 10 per cent solution 
of "formalin" will contain but 3.5 per cent of "formaldehyde," which 
is, of course, the reactive substance. Formaldehyde is an excellent 
disinfectant for sputum, urine and feces, and other excretions; a 5 
per cent solution of formalin (corresponding to about 2 per cent 
formaldehyde) in the proportion of 2 volumes of the disinfectant 
to 1 of the excretion will effect practical sterilization of feces within 
one hour. Fomites are steriKzed in the same manner. The fumes 
are irritating, and disinfection should not be practised in the sick-room. 
Essential Oils.— Essential oils have been used extensively in the 
past, particularly in the treatment of nasal and pharyngeal infec- 
tions, and for mouth-washes. Menthol, thymol and eucalyptol, the 
active principles of oil of peppermint, thyme and eucalyptus respec- 
tively, undoubtedly possess antiseptic and feebly germicidal properties. 
Cloves, cinnamon and other spices have been used for the preserva- 
tion of certain types of foods; their efficiency probably depends largely 
upon their content of essential oils. The expense of these substances 
compared with their efficiency as antiseptics makes their use practically 
prohibitive. 
Soaps.^— Cleanliness is a very important barrier to the spread of 
disease. Very few pathogenic bacteria upon exposed surfaces of 
rooms can survive an application of hot soap suds applied with a 
vigorous arm and a scrubbing brush. A 5 per cent solution of wash- 
1 Formaldehyde unites with ammonia and the amino-nitrogen of amino-acids to 
form stable compounds; there is relatively less action upon native proteins, however. 
2 See Walker, J. E.: Jour. Infec. Dis., 1926, 38, 127; 1924, 35, 557; 1925, 37, 181 for 
germicidal properties of soap. 
