466 APPENDIX 



water, etc. Add a drop of methylene blue in thin mucilage to the water 

 close to the animal. 



We study Daphnia as an advance epitome of animal functions, and 

 perhaps nowhere else might we find so clearly and easily displayed so 

 much basal physiology for the mere looking, without preparation of any 

 sort. We may readily behold in little Daphnia the fundamental portions 

 of the blood's physical composition and its circulation, respiration, nutri- 

 tion, the nervous system, muscular action, and reproduction (especially 

 embryology). We will divide our observation of these basal activities 

 orderly as follows : 



Expt. 12. The Blood and its Circulation. Careful watching of the 

 head-region, especially between the eye-muscles, shows clearly even with 

 a one-third objective the many-shaped one sort of blood-corpuscles of 

 this colorless blood. These are the amebocytes corresponding to the 

 leukocytes of man, but doubtless with even more functions to perform. 

 As the name implies, these cells have ameboid movements. They are 

 relatively few in number, as may be seen; compare the 10,000 to the 

 cubic millimeter present in man's blood. If any respiratory pigment 

 like hemoglobin exists in Daphnia's blood it is colorless. Its rate of 

 circulation may be clearly seen by means of the corpuscles, as also its 

 general course about the wide membrane-formed sinuses under the shell. 

 The most conspicuous of these channels lies dorsad to the alimentary 

 canal and in it pulsates the heart. Isolate some blood and examine its 

 corpuscles. 



Daphnia's heart (see Dearborn, Med. News, March 21 and 28, 

 1903 etc.), is as simple structurally and functionally as a heart well 

 could be. It consists almost wholly of two series of smooth muscle- 

 cells arranged on both sides of the dorso-ventral plane so as to form an 

 ovate saccule open in front and with an ostium (for the blood's entrance) 

 in the middle of each side. By the simultaneous shortening of these 

 blunt fusiform cells the heart is made to pulsate. The rate usually is 

 about 240 per minute, but it varies greatly with the temperature. The 

 embryonic rate (see the brood-sac) is less rather than greater than the 

 adult rate. The pulse-rate persists until the heart entirely stops, and is 

 readily variable by the ordinary physiological salines. Irritation with a 

 fine needle in the abdominal fold stops or inhibits the pulsations instantly. 

 Study the cells of the heart, and its movements. 



Nicotine in 2 per cent, aqueous solution gradually slows and stops the 

 heart in diastole after several minutes of great irregularity. Digitalis 

 in 3 per cent, aqueous solution of the tincture slows and invigorates it, 

 but makes it irregular. Curare injected into circulation stops the heart 

 at once. Chloral increases the power and the length of the diastole 

 and slows the pulse-rate. Some of these drugs and many saline in- 

 fluences change the functional size of the heart in a way to strongly 

 suggest the presence of the tonus which is so conspicuous, for example, 

 in the turtle's heart and probably present in all hearts a slow tonal 

 contraction and relaxation beneath the pulsations. The existence of a 



