recording the progressive growth of animals. This is a chart taken from the records of my friend, Dr. Henry P. Bowditch, showing the growth of school children in Boston. Here we have, in the lower part of the figure, the two curves of growth in weight. The upper curve if; the weight of boys. We can follow it back through the succession of years down to the age of five and one half years, when the records begin. The child weighs, as you see, a little over forty pounds at that time. When the boy reaches the age of eighteen and one half years, he approaches the adult size, and weighs well over 130 pounds. Here then we see growth represented to us in the old way, the progressive increase of the animal as it goes along through the succession of years. Now this is a way which records the actual facts satisfactorily. It shows the progressive changes of weight as they really occur; but it does not give us a correct impression of the rate of growth. Concerning the rate of growth, some more definite notion must be established in our minds before we can be said to have an adequate conception of the meaning of that term. It is from the study of the statistics of the guinea-pigs, and of other animals, which I have since had an opportunity of experimenting with, that we get indeed a clearer insight as to what the rate of growth really is and really means.
I should like to pause a moment to say that when I first published a paper upon the subject of growth, it, fortunately for me, interested the late Dr. Benjamin Gould. The experiments which I had made and recorded in that first publication came to a sudden end, owing to a disaster for which I myself was personally not responsible, by which practically my entire stock of animals was suddenly destroyed. Dr. Gould, after consulting with me, proposed that I should have further aid from the National Academy of Sciences, and through his intervention I obtained a grant from the Bache fund of the academy. That liberal grant enabled me to continue these researches, and this is the first comprehensive presentation of my results which I have attempted. In this and the subsequent lectures, I hope that enough of what is new in scientific conclusions may appear to make those to whose generosity I am indebted feel that it has been worthily applied. I can not let such an occasion as this pass by without expressing publicly my gratitude to Dr. Gould for his encouragement and support at a time when I most keenly appreciated it.
If animals grow, that which grows is of course the actual substance of the animal. Now we might say that given so much substance there should be equal speed of growth, and we should expect, possibly, to find that the speed would be more or less constant. I can perhaps illustrate my meaning more clearly, and briefly render it distinct in your minds, by saying that if the rate of growth, as I conceive it, should remain constant, it would take an animal at every age just the same, length of time to add ten per cent, to its weight; it would not be a
