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Page:Popular Science Monthly Volume 61.djvu/204

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198
POPULAR SCIENCE MONTHLY.
Time milt had
been in water.
Minutes.
Percentage of
fertilization.
Time milt had
been in water.
Minutes.
Percentage of
fertilization.
 ¼ 98 4 0
 ½ 88 5 0
1 38 6 0
 4 7 2
2  8 8 0
3  8

Similar experiments were performed with the ova, to determine their susceptibility to fertilization after being immersed in water for various periods. The following results were obtained from one series, which are typical of the others:

Time ova had
been in water.
Minutes.
Percentage of
fertilization.
Time ova had been
in water.
Minutes.
Percentage of
fertilization.
 ¼ 98 4 4
 ½ 96 5 4
1 95 6 0
68 7 1
2 57 More than 7 0
3 17

The average salmon produces about 6,000 ova. In artificial propagation from 5 to 20 per cent, cannot be spawned. These can be removed only by slitting the fish open, in which case a considerable quantity of blood is mixed with them. If the blood is not washed off, the fertilization cannot be made complete, as many of the ova become surrounded with clotted blood. But, if the blood is washed off with water, the ova immediately become turgid and not susceptible of fertilization. The difficulty was overcome as follows:

Among the many experiments testing the vitality of the ova and their susceptibility to fertilization under various conditions, one determined their reaction to normal salt solution. By normal salt solution, is meant water of the same degree of saltness as the body fluids, which in the case of the salmon we assumed to be .75 of 1 per cent., no chemical determinations having been made. Ova were spawned into a pan containing normal salt solution, and after various periods of time a few were removed and spermatized in the ordinary manner, with the following results:

Time ova had been
in salt solution.
Minutes.
Percentage of
fertilization.
Time ova had been in
salt solution.
Minutes.
Percentage of
fertilization.
2  99  8 99
4 100 15 97
6 100 25 86