��THE POPULAR SCIENCE MONTHLY.
��presence of others. Some substances, inor- ganic or organic, when added to the solution, are neutral ; others evolve the oxygen and are themselves unchanged ; a third kind evolve the oxygen, and with that some of their own contained oxygen ; and a fourth kind absorb the oxygen. Thus, with oxide of iron there is no action ; with black oxide of platinum a taper can be lighted from the oxygen thrown off ; with permanganate the action is very brisk, and oxygen is thrown off from both substances; and arsenious acid absorbs oxygen from the solution. Dr. Kich- ardson has found peroxide of hydrogen use- ful in a large number of diseases ; among them are consumption, whooping-cough, ul- cers and purulent exudation, syphilis, dia- betes, ana3mia, rheumatism, and others, his experiments with which, and his methods of application, are described in a paper recently read by him before the Medical Society of London.
Origin of Caste. — The origin of caste in India was traced by General T. Dennehy, in the International Oriental Congress, probably to the contact of the Indo-Aryans on their first migration with the uncouth, uncivilized abo- rigines of the countries which they traversed. The Aryans were even then highly civilized and careful as to personal cleanliness and religious observances, and naturally shrunk against contact with the unwashed aborigi- nes. They were particularly so with regard to food, and hence arose the first manifesta- tions of caste in the exclusion of strangers from their meals. This custom grew with years to be a cherished observance, and what was first a measure of hygienic precau- tion became an article of religious belief. The later developments of caste corresponded with the guilds of European countries so prevalent in the middle ages. New castes were seen growing up in India as new neces- sities arose. For example, since the estab- lishment of railroads it had been necessary to find pointsmen (switchmen) and firemen; and these men, being anxious to preserve the emoluments of their posts in their own families, were now actually crystallizing into a new caste. The views expressed by M. C. A. Fret, though differing from these, were not inconsistent with them. He discerned the working of evolution in caste. The Indo-
��Europeans formed at an early period a social hierarchy which continued in full force long after the language spoken by them had ceased to be a living tongue. The general ignorance prevailing in primitive times neces- sarily involved the evolution of a priestly or teaching caste — the Brahmins. The ne- cessity of having men always on guard against the attacks and invasions of neigh- boring races with different tendencies led to the warrior class or caste. These two leading castes represented the two leading principles in the constitution of civilization — the religious and the military. The civil principle, properly so called, did not come into existence till a later period.
Little Annoyances and Health.— Such
matters as water supply, sewerage and drain- age, streets and pavements, including means of rapid transit, parks, and open spaces, lighting, provisions for the dead and for those affected with contagious disease, and the sale of improper food and drinks, are classed by Dr. John S. Billings, in his address on Public Health and Municipal Government, as variables under municipal control, many of which have a powerful influence on the health of the people. A large part of the discussions as to the best way to arrange and manage them, or as to whether in any par- ticular place at a particular time the munici- pality is doing its duty with regard to them, turn on sickness and death-rates. It should be borne in mind, however, Dr. Billings adds, that no sharp dividing-line can be drawn between comfort and health ; that there are many things — such as noise, dust, offensive odors, rough streets, etc. — the influence of which upon sickness and death-rates it would be at present difficult or impossible to demon- strate, at least to the satisfaction of a court of law, which yet add materially to the burdens of life of those who are subjected to them, and may in some instances turn the scales between life and death. The human body in some diseases may be likened to a heavy railway train going up a very steep grade. If the fire under the boiler can be kept bright and clear, if the fuel and water hold out, and the engineer is skilled and careful to get the benefit of every pound of steam power developed, then the train will just reach the top of the hill, provided there