Maech 29, 1907] 



SCIENCE 



485 



cause the apparent disturbance in the re- 

 spiratory mechanism and not so much the 

 mechanical interference with the ventila- 

 tion of the corresponding lung. Since the 

 classical experiments of Regnault and Rei- 

 set many investigators have stated that 

 compression of one lung or a unilateral 

 pneumothorax exerts very little influence 

 upon the respiratory exchange of gases. 

 Hellin reported recently a series of experi- 

 ments on rabbits in which the right lung 

 was completely removed. The right lung 

 of the rabbit has four lobes and is much 

 larger in volume than the left; that means 

 that more than one half of the lung tissue 

 was removed. Most of the animals sur- 

 vived the operation and some lived a year 

 and longer. Except for a temporary mod- 

 erate dyspnoea lasting only an hour or two 

 the animals were in a normal condition, 

 and the respiratory quotient continued to 

 be after the removal of the lung exactly as 

 it was just before the operation. We see 

 then that the normal process of respiration 

 can be carried out with at least one half 

 of the lung tissue and probably with a good 

 deal less. "We have here with regard to 

 the quantity of tissue a factor of safety 

 equal at least to two, which does not ap- 

 pear to be an excessive margin considering 

 the importance of the function which that 

 tissue has to carry out. 



Of the bilateral organs of reproduction 

 we know from numerous surgical opera- 

 tions that the removal of one ovary or of 

 one testicle does not interfere in the slight- 

 est degree with the corresponding functions 

 of the individual. For the female oi^ans 

 it has been frequently established that even 

 a small part of one ovary is sufficient to 

 carry on the function of menstruation and 

 conception. In fact, there are a number 

 of reliable cases on record in which preg- 

 nancy occurred after the removal of both 

 ovaries, which cases were explained by the 



assumption that some particle of normal 

 ovarian substance was caught in the liga- 

 ture and retained in the body, and this 

 fragment was then sufficient to carry out 

 the function of ovulation and conception. 



For the testicles we may safely assume 

 also that a small fragment of one testicle 

 left in the body would be capable of carry- 

 ing on the function of reproduction. But 

 I did not come across experimental or 

 surgical data which directly bear out this 

 assumption. There are definite data with 

 regard to the secondary sexual character- 

 istics in fowls. If in the process of castra- 

 tion some fragment of one testicle is left, 

 the cock, according to Foges and others, 

 does not lose the comb and other secondary 

 sexual characteristics. However, these sec- 

 ondary characteristics are probably con- 

 nected with the internal secretion of these 

 organs, and their persistence might not be 

 a sufficient proof for the persistence of the 

 function of reproduction. At any rate, it 

 is sufficiently evident, especially as will be 

 seen later, that the tissues of the organs of 

 reproduction are greatly in excess of the 

 maximum need of the chief function of 

 these organs. 



Among the bilateral organs there are two 

 whose functions are carried on exclusively 

 by internal secretion, I mean the thyroid 

 and the adrenal glands. We do not notice 

 their activity while they are present, but 

 we recognize their importance by the seri- 

 ous elf ects which follow their removal. 

 The complete removal of both thyroid 

 glands is followed either by acute symp- 

 toms of a tetanic type or by chronic states 

 which are known under the names of myx- 

 oedema and cretinism. It is, however, a 

 well-established fact that the removal of 

 four fifths or even five sixths of both thy- 

 roids is not followed by perceptible conse- 

 quences, which means that one fifth or one 

 sixth of the entire gland is amply sufficient 



