1865.] The Laws of Health. 153 



question of the quantity of fresh air required for healthy existence. 

 After giving the result of a variety of experiments in the quantity of 

 carbonic acid expired, and of oxygen consumed, by a human being in 

 twenty-four hours, he comes to the conclusion that in order to render 

 the products of expiration and transpiration uninjurious, a human 

 being should be supplied with 2,000 cubic feet of fresh air every 

 hour. In order that anyone may see how far short of a proper 

 standard of pure air they are breathing, they have only to calculate 

 whether the room they sit, sleep, or do their business in, will allow 

 of the egress of 2,000 cubic feet of bad air, and the ingress of the 

 same quantity of fresh air for every person occupying them ; if not, 

 they will suffer. This is one of the great problems to be solved, 

 in order to secure a healthy existence. One great difficulty that meets 

 us in every direction is the necessity of warmth. We try by our feel- 

 ings to measure the necessity of warmth against fresh air, and as cold 

 is much more easily appreciated than bad air, we secure warmth at a 

 frightful expense. 



A great evil which has been recently added to our civilization, is 

 the use of gas. Its economy, its brilliancy, has led to its use in almost 

 every household, and there can be no doubt that its use has increased 

 our dangers from impure air fivefold. Fortunately its use has not 

 extended to the lowest classes, or its effects would be frightful. 

 The cause of the deadly influence of gas is, that each gas-light con- 

 sumes as much oxygen, and gives out as much carbonic acid, as five 

 human beings. It is thus that gas has given the results of overcrowd- 

 ing to houses, that previous to its use were free from any such effects. 

 Nothing but the universal adoption of a system of carrying directly 

 out of our rooms, by some means or another, the products of the com- 

 bustion of these deadly consumers of oxygen, can prevent their dis- 

 astrous effects on the health of the community. 



Air, however, is not alone rendered impure by the respiration of 

 human beings and combustion, but by various effluvia. These are 

 organic and inorganic. The organic are living, as microscopic plants 

 and animals, and the poisonous molecules of contagious diseases, as 

 typhus, typhoid, and scarlet fever ; and dead, as the poisonous mole- 

 cules given off from decomposing animal and vegetable matters. All 

 these are treated of by Dr. Parkes, and valuable practical directions 

 are given for the ventilation of rooms, and for the getting rid of 

 poisons in the air. 



We cannot, however, follow Dr. Parkes through the remainder 

 of his book. The space given to the consideration of food is very 

 large, and is, perhaps, the only part of the work in which the author 

 has been fully anticipated by other writers. At the same time we 

 recommend the disciples of Banting to turn to Dr. Parkes's volume if 

 they want to see the dangers into which they are likely to fall, and 

 the absurdity of the statement made by Mr. Banting himself, that the 

 subject of diet was not understood, and had not been studied by 

 medical men. 



The chapter on dress is well worth attention at the present day, 

 when our Volunteers are likely to set the fashion of how a man ought 



