860 SPECIAL PHYSIOLOGY. 



pure air; for in this depressed state of the respiratory and other 

 functions, the need for fresh air is less felt, and habit reconciles the 

 senses, and dulls the perception, to the effects of the suicidal practice 

 of inhaling an atmosphere poisoned by one's self. Persons accustomed 

 to hot, close, unventilated rooms, loaded with a vitiated atmosphere, 

 do not recognize, either by smell, or by the sensations of enfeebled 

 bodily health and infirmity, the effects of the impurities which they 

 breathe. Moreover, they often believe themselves, and are regarded 

 by others, to be in an average state of health ; but the onset of an 

 epidemic, or of a contagious disease, reveals their want of power to 

 resist morbid influences. As a most serious predisposing cause of 

 disease and mortality, during such visitations, the overcrowding of 

 rooms, whether large or small, public or private, is fully recognized. 



The overcrowding of the population in parts of towns or villages, is always 

 very inimical to health. This is doubtless partly to be explained by the fact, 

 that it is the poorer classes, less well provided for, in every way, which occupy 

 such neighborhoods ; it is also partly due to the closer proximity of the in- 

 habitants to each other, and to their increased liability, from this circumstance, 

 to communicate diseases to one another. But the increased accumulation, 

 within a limited space, as in towns, or in the immediate neighborhood of dwell- 

 ings, as in villages, of the excreta, and of the waste animal and vegetable 

 matters of the food, which constitute, when undergoing decomposition, sources 

 of contamination to the air, cannot be here disregarded. Indeed, it has been 

 shown that whereas, in the open country near Manchester, the quantity of 

 organic matter in the air, is only 1 grain in 200,000 cubic inches, in the con- 

 fined and overcrowded districts within that city, the proportion is, 25 grains 

 in the same quantity of air. 



The open ditches for drainage, and the heaps of garbage and refuse, in vil- 

 lages, and the uncleansed sewers, defective drains, and untrapped water-closets 

 and sinks, in cities and towns, by admitting the escape of foul air into the en- 

 virons, the lanes, the streets, or the houses themselves, are serious causes of 

 insecurity to health. Sewer-atmosphere usually contains sulphuret of ammo- 

 nium, or ammonia and sulphuretted hydrogen, frequently carburetted hydro- 

 gen, and besides these, it is loaded with organic matter, decomposing or putres- 

 cent, mixed with the spores of fungi, and with the minute living organisms 

 known as bacteria, or, at any rate, with the organizable material in which these 

 are generated. A house into which such an atmosphere is conducted, by an 

 untrapped sink, or other defect, resembles, when closed at night, an inverted 

 bell-jar over an open gas-pipe, or a receiver specially connected with the sewer, 

 which acts as a retort for the evolution of poisonous vapors. It is necessary to 

 exclude such chances of contamination of the air inside a dwelling-house ; and to 

 prevent also the contamination of the atmosphere in the immediate vicinity of 

 the dwelling from which the internal supply for ventilation is derived. This is 

 the immediate sanitary purpose of a perfect system of sewerage and drainage. 

 Water is, for large cities certainly, and perhaps also, wherever available, the 

 most cleanly and convenient vehicle for carrying away the excretory products 

 of the inhabitants : the sewers should themselves be ventilated. Great care is 

 needed to prevent the sewerage matter from contaminating wells, or other 

 sources of drinking-water ; for water is thus, as easily, and much more insidi- 

 ously, contaminated than air. Earth closets are suitable for the country. 



It seems probable, though but little is certainly known on these subjects, 

 that zymotic diseases, whether contagious or epidemic, spread themselves, at 

 least to a great extent, through the air, and enter the body through the lungs ; 

 moreover, it is possible that the agents which cause them, have, if not an or- 

 ganic germinating, at least a chemical self-multiplying property, and that im- 

 purities, whether in solid bodies, in water, or in air, may form a nidus for such 

 increase or growth. 



