DEVELOPMENT OF THE HUMAN BEING 
the means employed and the results reached to speak of 
the X-ray treatment of the sex cells of certain plants, as 
reported by Goodspeed and Olson. With a Coolidge X-ray 
tube operated at 50,000 volts, the flower buds of the plant 
Nicotiana tabacum,variety purpurea,were treatedin January 
for ten- and twenty-minute intervals. Of over 1,000 plants 
raised from these seeds more than twenty per cent were 
variant from the normal. In one lot of 168 plants, 136 were 
variant. A majority of the variants were decidedly abnor- 
mal in such characters as stature, leaf shape, and flower 
structure. Many of the new forms were completely fertile. 
In some variants the chromosomes themselves were found 
by microscopic examinations to be visibly altered. 
The development of the individual human being enters 
a new phase with birth. Ceasing to depend upon the moth- 
er’s circulation for nourishment and excretion of waste 
matter, the infant begins to employ its lungs to vitalize the 
blood with oxygen, and its digestive organs to assimilate 
food taken for the first time through the mouth. At this 
epoch of radical change in habit, let us pause to compare 
the status of the infant with that which has preceded and 
that which is to follow. As regards age, length, and weight, 
the average prenatal growth has been summarized as follows: 
AGE LENGTH WEIGHT 
Months Centimeters Inches Grams Pounds 
0.47 0.015 0.006 
0.63 OW13 0.05 
Ted. 0.88 0.35 
D5 1.6 0.63 Dk 
1.8 BES 1.0 4 0.009 
2% 8 oT 20 0.045 
35 14 ns 120 0.26 
Ane 22 8.3 285 0.63 
5 5 31 12 635 1.40 
6.5 36 14 1220 Deg) 
a5 42 =i eo x | 
a6 48 1g 2240 4.9 
9.5 50 20 3250 We 
