The Pigmentary Effector System. 



323 



severally with the above strengths. The first and fifth doses were, it will 

 be noted, quantitatively equivalent to the second and third in the foregoing 

 experiment. At the end of half an hour the first two pairs (0 - l per cent, and 

 O075 per cent.) were intensely dark ; the others showed but slight, if any, 

 perceptible change. Microscopic examination of pieces of the skin showed 

 that in the first two pairs the melanophores were expanded, whereas in the 

 remainder they were contracted. It may be well to observe parenthetically 

 in this connection, that the terms contraction and expansion are used in a 

 purely descriptive sense throughout this paper, without prejudice to the 

 controversial issue, to be dealt with subsequently it is hoped, whether the 

 pigment cell as a whole contracts and expands, or whether on the other hand 

 the appearance is due to the independent migration of the pigment granules. 



The above experiments illustrate two significant aspects of the pituitary 

 melanophore reaction : («) there is a fairly definite end point ; and (V) it is 

 extremely sensitive when the clinical dose is taken as a basis of comparison. 

 Since 05 to 1 c.c. are usually administered clinically {e.g., in parturition), it 

 will be seen that less than a thousandth of the clinical dose, or - 0004 c.c. of 

 the commercial (21 per cent.) extract, suffice to evoke the response.* 



To obtain more crucial data it will be necessary to substitute for the crude 

 method of injection via the dorsal lymph sac the intravenous or intraperitoneal 

 operation. Considering the extreme technical facility of this method of 

 testing the activity of pituitary preparations, the rapidity with which it can 

 be carried out, the simplicity and cheapness of the materials employed and 

 finally the probable identity — as will be seen later — of the melanophore and 

 uterine stimulants, it is not premature to suggest in this place ' that the 

 pituitary melanophore reaction merits the fullest consideration as an 

 alternative to the very elaborate methods now employed for the standardisa- 

 tion of clinical preparations. It would be well moreover to explore the 

 possibility of employing strips of frog skin as Hooker was successful in 

 culturing the latter. It should then be possible to eliminate the factor of 

 individual variation as a source of error. Spaeth emphasised this point in 

 relation to the use of fish scales : the frog has the merit of being much more 

 easily obtained and reared ; and since excitement and mechanical stimulation 

 ordinarily cause the frog's pigment cells to contract, everything favours the 

 success of manipulation. 



4. Relation of the Melanophore Stimulant to other Pituitary Autocoids. 



It is now generally recognised that the diverse responses evoked by extracts 

 of the posterior lobe of the pituitary gland are not due to a single autocoid. 



* 0"21 gr. fresh infundibular substance in 1 c.c. 



2 A 2 



