640 



NA TURE 



[October 25, 1906 



Ijressure on t-ither side iif the index is equal, a circum- 

 stance wliich tends to reduce to a minimum the errors 

 due to inertia of the index, and this is of g^reat advant- 

 aj^i-e in estimatinjj the diastolic blood-pressure. 



In a valuable booklet recently issued by Dr. Oliver ' 

 on blood-[3ressure g-auging, he sets forth some of the 

 more important results he has arrived at by means 

 of this ing-enious instrument. This physician attaches 

 considerable importance to the study of the pressure 

 in the smallest arteries and capillaries bv means of 

 a digital bag. He finds that while arteriolar dilata- 

 tion lowers the pressure in the larger arteries by 

 lessening peripheral resistance, it tends to augment 

 that in the capillaries and pre-capillarv vessels bv 

 increasing their supply of blood. During muscular 

 exercise, on the other hand, the pressure throughout 

 the entire length of the systemic arteries is increased, 

 owing to the fact that the dilatation of the arterioles 

 is accompanied by a considerable augmentation of 

 cardiac action. The essential circulatory change 

 attending upon digestion, so far as the systemic 

 system is concerned, is, according to Dr. Oliver, an 

 increment in the capillary and pre-capillarv pressure, 

 whereby an increase of lymph-exudation is effected, 

 and the products of recently digested food thus 

 speedily conveyed to the tissues. Such an augment- 

 ation in the exudation of lymph he claims to have 

 demonstrated. 



Of special interest are Dr. Oliver's observations on 

 the blood-pressure of the aged and elderlv. With 

 advancing years the smaller vessels tend to become 

 rigid and impervious, and thus to lose their power of 

 dilating in response to physiological requirements, 

 such as digestion and muscular exercise. When this 

 happens the blood-pressure in them is found to be 

 habitually low, and to fail to rise readilv during 

 digestion, or as the result of administering such a 

 drug as nitroglycerine, which normallv dilates the 

 smaller arteries. In this way the phvsician is able 

 to gauge the condition of the blood-vessels with a 

 precision which was quite impossible with the older 

 methods. In cases of premature degeneration of the 

 blood-vessels. Dr. Oliver believes that much mav be 

 done to check the degenerative process, .\mong the 

 methods he employs to this end is the administration 

 of certain substances the deficiency of which in blood 

 is thought by some to be largelv responsible for the 

 phenomena of senility. 



These brief references sufifice to show the firactical 

 value attaching to the clinical studv of blood-pressure. 

 The student in this important branch of investigation 

 will find great help from Dr. Oliver's book, the more 

 so that only salient and practical points are dealt 

 with, and these in clear and simple language. 



MENDEL'S CORRESPONDENCE WITH 

 NAG ELI. ^ 

 'T'HESE letters constitute a valuable addition to the 

 -'■ pile of literature that has accumulated under the 

 name of one of the most remarkable figures in the 

 history of biology — Gregor Mendel; for we doubt if 

 ever has so great a fame been built on the contents 

 of a single short paper. The fact that this paper 

 remained unknown from 1865, when it was published, 

 until 1900, when it was rediscovered, is both the 

 measure of how much Mendel was before his time 

 and the reason for the uniqueness of the picture of 

 him which presents itself to the eves of most of us. 



1 "Studies in Blood-pre^-iure : Physiolngical and Clinical." By Dr. 

 George Oliver. (London : H. K. I.ewi<, iqo6.) Price as. 6ri. net. 



- "Gregor Mendel's Briefe an Carl Nageli, 1866-73. Ein Nachtrag zu 

 den veroffentlichten Bastardierungsversuchen Mendels." Edited by 

 C. Correns. Abhandl. d. K. S. Gesellsch. d. Wissensch., math.-phvs, 

 KI. xxix. iii. Pp. 189-264. (Leipaig: B. G. Teubner, 1905.) Price 



W'e h.ive, it is true, neat and compendious biographies 

 of Mendel, but they reveal to us little of the man 

 himself, and it is still a distant and mysterious monk 

 that appears to us, with his classical peas in his 

 cloister garden. The value of these letters is that 

 they lift the veil for us here and there, and extend 

 to us an invitation to a " private view " of his work, 

 and offer us an opportunity of a nearer acquaintance 

 with its author. 



The correspondence was begun by Mendel, who 

 wrote to Nageli on New Year's Eve, 1866. In this 

 letter he referred to Nageli 's great services to the 

 study of hybrids occurring in nature, mentioned his 

 own results with peas, gave an account of some new 

 experiments he was starting with the hawksweed, 

 and ended with what was probably the reason for his 

 writing, an a|)peal for heljj and advice with these 

 experiments. 



Nageli answered on February 24, 1867, addressing 

 Mendel as Verehrtester Herr College. He recom- 

 mended some hawksweed species for the proposed ex- 

 periments, but the chief interest the letter has for us 

 lies in the criticism which it contains of Mendel's well- 

 known formulEe. Nageli said : " Die Formeln diirften 

 Sie wohl ebenfalls fiir empirische halten, da dieselben 

 als rationellen nicht zu erweisen wiiren." Mendel's 

 replv to this criticism is a little difficult to under- 

 stand, and Prof. Correns remarks in a footnote, " Icli 

 weiss nicht, ob Mendel hier das, was Nageli unter em- 

 pirischer und rationellcr Formel meinte, ganz ver- 

 standen hat." But I suggest Mendel's reply becomes 

 intelligible if we divide it into two sections (the first 

 of which ends with the sentence to which Correns's 

 note is appended), and legard each section as an 

 answer to one of two interpretations, of the criticism, 

 by Mendel, who I imagine was not quite sure what 

 Nageli meant. In the first part of his answer Mendel 

 interprets the criticism as meaning that the simple 

 foriiuils, in which only one pair of characters is 

 concerned, are "empirical," and that the complex 

 ones, in which many are concerned, are "rational." 

 I think we mav be pretty sure that Nageli did )\<>t 

 mean this; however, I am not here concerned with 

 what he did mean. 



Nor do I stop to discuss what Nageli may have 

 meant when I come to consider the second section 

 of Mendel's replv. The point is that it begins with 

 ihe words " Was schliesslich die .\ngaben iiber die 

 \'erschiedenlieit der von den Hybriden gebildeten 

 Keimbliischen und Pollenzellen betrifft. ..." Mendel 

 is discussing an entirelv different subject now, and he 

 shows unconsciouslv by this fact that it never occurred 

 to him that Nageli might mean bv his criticism that 

 while of course it was impossible to deny the nu- 

 merical proportion of the different categories 

 (iD : 2DR : iR), that was a very different thing from 

 stating one's belief that the suggested interpretation 

 of that proportion (the random union of 



50 , J) + 50 R with 50 -D -I- 5o°;.R) 



was true, and that it was very desirable that these 

 two entirely different things should not be confused. 

 Nageli may or may not have meant this, but the 

 point of interest is that it did not occur to Mendel 

 that he might have done, which shows that so far 

 was he from confusing these two things that the pos- 

 sibilitv that he might have done never occurred to 

 him as an interpretation of Nageli 's criticism. 



I have discussed this at some length because such 

 confusion is not rare among modern students of 

 heredity. 



This'second letter of Mendel's was accompanied by 

 several packets of peas, which were sent to set 

 Nageli 's doubts at rest. 



NO. 1930, VOL. 74] 



