Charles Sedgwick Minot, an embryologist, (d. 1914, _a.e._ 62) devoted most of his maturer years to a study of the phenomena of growth, keeping and daily weighing many young animals, especially guinea pigs, and he has left us a good compendium of his life work.[172] Stated in the most general terms, he held that old age and death were progressive phenomena that began in the individual with life itself, that the best method of measuring vitality was the rate of growth, and that this constantly diminishes and finally ceases. As soon as, for example, guinea pigs recover from the disturbances caused by their birth, which are great and last two or three days because they are born at a very advanced stage of development, they add from 5 per cent to 6 per cent to their weight during a single day. But this percentage diminishes, so that by the end of the first month they add only 2 per cent; at ninety days, only 1 per cent; and the diminution continues, rapidly at first and then more slowly. Calculating the time to make successive additions of 10 per cent, there are twenty-five of these additions; and not until we reach the seventeenth addition do we find nine days or more necessary. The twenty-second addition takes four days, the later ones being somewhat irregular. The first ten per cent increment often comes in two days. Chicks, too, are born highly developed, and so lose during the first day. Then the daily percentage of increase is greater than in the guinea pig. From the sixth to the tenth day inclusive the average is nearly but not quite 9 per cent; at the end of the third month, only 2 per cent. Rabbits are born very immature and, being less developed, grow more rapidly. The average for males of the first five days of growth is over 17 per cent. The rabbit thirty days old has about the same daily percentage of increase as the new-born guinea pig. The human child takes 180 days to double its weight; a horse, 60; a cow, 47; goat, 19; pig, 18; sheep, 10; cat, 9½; dog, 8; rabbit, 6–7, these rates depending, in part, on the quality of the mother’s milk.