Page:Popular Science Monthly Volume 33.djvu/733

Rh in turn draws from the air which has been swallowed into the stomach. This organ becomes, then, in the diver, a reservoir of air. It is evident from these observations that if persons who have been trained to diving can not remain under water more than four minutes without exposing themselves to great dangers, drowning men who struggle and inspire water can endure so long only under extremely favorable circumstances. The lesson is also taught that divers should not inflate their lungs before plunging, but should swallow air, which then passing from the stomach to the lungs will support respiration during a definite period of immersion.

Exhaustion from Rowing-Contests.—Prof. W. P. Trowbridge has discussed, in a paper read before the New York Academy of Sciences, the question "whether the excessive training for long-distance boat-races and the violent and long-continued muscular and nervous exertions incident to these contests do not in reality result in unnecessary and hurtful exhaustion during a race, and frequently in permanent injury to the contestants." Prof. Trowbridge says: "The boat-race involves the action of all the muscles, those of the legs, arms, and shoulders, as well as of the back; and hence the demands on the heart and lungs are the greatest possible. The work which a rower performs in each minute of a four-mile race is easily calculated. The distance—21,120 feet—is traversed in about twenty-one minutes. The speed is therefore practically about 1,000 feet per minute. At this speed the resistance to the boat in the water is about 75 pounds. This resistance has been determined experimentally as well as theoretically in England, the average result being 75 pounds. The work per minute for eight men is therefore 75,000 foot-pounds, or 9,375 foot-pounds (42 foot-tons) for each man per minute. At the rate of 350 foot-tons in ten hours, the day-laborer performs work at the rate of only six tenths of a foot-ton per minute. The rower in the boat-race, therefore, performs work each minute equivalent to the work of seven strong laborers, or at the rate of nearly one third of a theoretical horse-power each minute during the race. The question now recurs: For how long should these extraordinary efforts be sustained? Four miles in distance and twenty-one minutes in time mark extreme limits of endurance according to all experience in boat-racing; and if races are practically decided at the end of the third mile, or whether they are so decided or not, the fourth mile is a test not of skill and muscular strength, but of the hearts and lungs of the crews. This is rather serious business. Is it quite rational to make the ultimate endurance of these vital organs in a dozen young men a matter of sport and amusement? It is hardly to be expected that any boat-crew will initiate a movement to reduce the length of course from four miles to three; to use an appropriate expression, they 'would die first.' Such a movement might be looked upon as a confession of weakness; but when the suggestion comes from an outsider it is made to all alike, and may at least be discussed with possible profit."

Sanitation among the Negroes.—At a Public Health Conference held in Louisville, Ky., Bishop C. C. Penick read a paper in which he says: "It was startling to the North and the South alike, when the census of 1880 showed the tremendous increase among the colored people, and the cry of alarm ran through the land lest in the near future the black should be the dominant race in this country. The world did not recognize the fact that the great source of Southern wealth had consisted in making the negro prolific. Everything that could be done was done to eradicate all the diseases threatening to interfere with this object. In short, a man's negroes were a man's money, and you may just rest assured that he looked after them." When the race was released from bondage, its momentum carried it up to those startling figures of the 1880 census—figures which Dr. Penick thinks we shall never see again, for there is no longer an intelligent class which has a direct pecuniary interest in the health of the negroes; the latter are leaving the plantations for the less healthful surroundings of the towns, and the enfeebling vices of the town are spreading into the country. In a pamphlet by Dr. G. B. Thornton, of Memphis, it is stated that, although the white population of that city slightly exceeds the black, yet in 1880 a fifth more blacks than whites died, in 1881 a fourth