Chap. XXIII. 



CONDITIONS OF LIFE. 



289 



relation to any particular variation, in comparison with the 

 organisation or constitution of the being which varies. 



It is known from the labours of Geoffroy St. Hilaire, and 

 recently from those of Dareste and others, that eggs of the fowl, 

 if shaken, placed upright, perforated, covered in part with 

 varnish, &c, produce monstrous chickens. Now these monstro- 

 sities may be said to be directly caused by such unnatural con- 

 ditions, but the modifications thus induced are not of a definite 

 nature. An excellent observer, M. Camille Dareste, 57 remarks 

 " that the various species of monstrosities are not determined 

 "by specific causes; the external agencies which modify the 

 " development of the embryo act solely in causing a pertur- 

 " bation — a perversion in the normal course of development." 

 He compares the result to what we see in illness : a sudden chill, 

 for instance, affects one individual alone out of many, causing 

 either a cold, or sore-throat, rheumatism, or inflammation of the 

 lungs or pleura. Contagious matter acts in an analogous manner. 58 

 We may take a still more specific instance : seven pigeons were 

 struck by rattle- snakes; 59 some suffered from convulsions; some 

 had their blood coagulated, in others it was perfectly fluid ; some 

 showed ecchymosed spots on the heart, others on the intestines, 

 &c. ; others again showed no visible lesion in any organ. It is 

 well known that excess in drinking causes different diseases in 

 different men ; but men living under a cold and tropical climate 

 are differently affected : 60 and in this case we see the definite 

 influence of opposite conditions. The foregoing facts apparently 

 give us as good an idea as we are likely for a long time to 

 obtain, how in many cases external conditions act directly, though 

 not definitely, in causing modifications of structure. 



Summary. — There can be no doubt, from the facts given in 

 the early part of this chapter, that extremely slight changes in 



■ 





5 ? ' Memoire sur la Production Arti- 

 iicielle des Monstrosites,' 1862, pp. 8-12 ; 

 'Becherches sur les Conditions, &c, 

 chez les Monstres,' 1863, p. 6. An ab- 

 stract is given of Geoffroy's Experi- 

 ments by his son, in his ' Vie, Travaux, 

 &c.,' 1847, p. 290. 



58 Paget, 'Lectures on Surgical 



VOL. II. 



Pathology,' 1853, vol. i. p. 483. 



59 'Eesearches upon the Venom of 

 the Kattle-snake,' Jan. 1861, by Dr. 

 Mitchell, p. 67. 



60 Mr. Sedgwick, in 'British and 

 Foreign Medico-Chirurg. Beview,' July, 

 1863, p. 175. 



U 



