KNOWLEDGE & SCIENTIFIC NEWS. 



[Mar., 1905. 



tion to generation through the viscid contents of the 

 g-erm-cells. Not only has this minute body concen- 

 trated within it the power of reproducing: ail the 

 anatomical details, but it must also transmit the pecu- 

 liar difference of temperament of animals, which has 

 g'iven to the cat and dog, for example, a disposition to 

 scratch and bite one another from time immemorable. 

 This conception of the g-crm-cell would lead us to re- 

 gard all animal and vegetable life as, in a sense, im- 

 mortal; for as every living thing contains within it the 

 power of producing this germ-cell, which in its turn 

 has the power of developing all the mental and ana- 

 tomical characters of the individual from which it is 

 derived, it may be argued that each living thing con- 

 tains within it the possibility of immortality. 



The next contribution to our modern views upon 

 heredity was made by Francis Galton. It is clear 

 that animals and plants all receive contributions to- 

 wards the characters they inherit, not onlv from their 

 two parents, but also from their four grand-parents, 

 their eight great-grand-parents, and in fact any an- 

 cestor may contribute characters down through a long 

 line of descendants, and hence that each individual 

 living thing must have inherited its characters from 

 many millions of ancestors. As the number of ances- 

 tors becomes doubled in each generation through 

 which we carry our enquiry, a simple calculation will 

 demonstrate the large number of ancestors from which 

 the individual has descended. In ten generations the 

 number exceeds two thousand, provided that there 

 has been no inter-marrying, and these figures increase 

 more rapidly the further back we carry our calcula- 

 tions. It is obvious that only a portion of any individual 

 ancestor could be transmitted. Thus if one parent has 

 dark hair and the other flaxen hair, the child could 

 not have both flaxen hair and dark hair; he must in- 

 herit either flaxen hair from one parent or dark hair 

 frorn the other parent, or he must inherit an inter- 

 mediate shade, receiving contributions from both 

 parents. Tlie child of a very tall father and a very short 

 mother will either be tall, short, or of some inter- 

 mediate heig-ht; he could not po.ssibly inherit the 

 characters of both parents in this respect. When we 

 realise the vast number of ancestors from each of 

 whom individuals may inherit characters, of those 

 contributed by all the rest, we see how complicated 

 the subject of heredity becomes. Rut the actual con- 

 tributions from ancestors seem to diminish as we go 

 backwards, for the contributions of the two parents, 

 one would .suppose, must equal those of the four grand- 

 parents, of the eight grcat-grand-parents, and so on, 

 since all the contributions combine into one individual. 

 It is therefore convenient to confine the enquiry to the 

 few later generations from which most of the charac- 

 ters have been received. Galton has endeavoured to 

 do this and to construct a law of heredity upon these 

 con.siderations. For this purpose he supposes that 

 each individual receives half his characters from his 

 two parents, one quarter from his four grand-parents, 

 and one-eighth from his more remote ancestors. This 

 assumption has received some support from materials 

 found in the stock of the Basset hounds, started some 

 years previously by .Sir Everett Millais. 



Gallon's hypothesis refers more particularly to those 

 characters which blend in the offspring. ITierc are 

 however, many characters which will not blend. The 

 coat colour of horses affords a good example of these. 

 One seldom sees horses whose coat colour cannot be 

 referred to one of the colours known as bay, chest- 



nut, grey, and so on; the eye colour in man affords 

 another example; we see brown eyes, blue eves, hazel 

 eyes, etc., but we seldom see tints which cannot at 

 once be referred to some one or other well defined 

 tints. When the eye colour of the two parents dif- 

 fers in tint, the child is stated to inherit this charac- 

 ter from one p;u-ent only, or from some one more re- 

 mote ancestor. A remarkable scries of experiments, 

 published in 1865, by Gregor iMendel, dealing more 

 particularly with these characters which do not blend 

 in the offspring, have lately been the subject of much 

 animated discussion. 



(iregor Joliann Mendel, born in Odran, in .(Vustrian 

 Silesia, was the son of well-to-do jicasants. In 1847 

 he was ordained priest, he studied physics and natural 

 science in Vienna, and returning to the cloister be- 

 came a teacher in the realschule at Brun. The im- 

 portance of his experiments, which were carried out 

 in the garden of his convent, were quite overlooked 

 until recently, when they were simultaneously redis- 

 covered by several investigators. The circumstances 

 connected with Mendel's researches appear to be 

 peculiarly like those of Sprengel's discovery of the 

 fertilisation of plants by the aid of insects, except 

 that, fortunately, Mendel docs not appear to have al- 

 lowed his enthusiasm for science to interfere with his 

 duties to his Church. Professor de \'rics called at- 

 tention to Mendel's remarkable memoir in 1890, and 

 Mendel's observations have since been confirmed by 

 other workers. 



Tliese investigations consisted in experiments made 

 by crossing varieties of plants differing from one 

 another in some important pair of characters, and re- 

 sulted in progeny being obtained which inherited those 

 characters according to fixed numerical rules; thus 

 Mendel's experiments give us ground for hoping to 

 discover the laws which control the forces of heredity. 

 He made a large number of experiments on the garden 

 peas, selecting varieties having pairs of characters 

 suited to his purpose. If the reader will observe the 

 seed-peas sold at seed-shops, he will notice that some 

 are almost round with smooth coats, whilst others 

 •are very much wrinkled; he will also discover, unon 

 splitting these seed-peas open, that the substance of 

 some of them is decidedly green in colour, whilst 

 in others it is bright-yellow. If he carries his enquiries 

 further and grows plants from these seeds, he will 

 find that some produce very inflated pods, whilst 

 others produce pods which do not exhibit this charac- 

 ter. It was because the common pea lent itself to 

 Mendel's purpose, by affording many such pairs of 

 characters, that he experimented upon it. Ilis results 

 were, in brief, after crossing many plants dilTcriiig in 

 some one pair of characters, in every case all the off- 

 spring could be referred to one or the other of the 

 parent forms. This character to which the offspring 

 'of the first cross could be referred, he called the domi- 

 nant character, and that which disappeared he called 

 the recessive character. From the seed obtained 

 from a first experiment he made a second, when he 

 found that only twenty-five per cent, of the offspring 

 from this second cross retained the dominant charac- 

 ter; the remaining sevcnty-fi\c per cent, having re- 

 verted to the recessive character; but he also found 

 that the offspring which remained dominant in this 

 ' econd experiment continued dominant in all subse- 

 qucnt generations. Carrying his experiments a stage 

 further with the seventy-five per cent., which had re- 

 verted to the recessive character, he found that one- 



