Szekessy Vilmos (szerk.): A Magyar Természettudományi Múzeum évkönyve 53. (Budapest 1961)
Pócs, T.: The calculation of the quantitative grade of efficacy of collecting and extracting methods of materials used in zoocoenology
Therefore x, expressing in this case the grade of efficacy of floating by a fatty alcohol sulphonate solution with reference to sifted soil containing mollusks 1 — BC 1 - 0,122 . 1,102 1 - 0,1344 0,8656 is : x = — - - = — — = = 0,7733, and 1 _|_ B 1+ 0,122 1 + 0,122 1,122 this value, being the efficacy-grade constant of the method, means that the grade of efficacy of the method is 77%, and thus there might have been 315 mollusk shells in the first sample. The value y, which expresses the grade of efficacy of the manual selecting method, is : y = === — = 0,4116. This is the efficacy-grade constant J 1 + C 2,102 of the method, therefore the grade of efficacy of the method is 41%. Multiplying the number of individuals received by the application of the method by the reciprocate value of the efficacy-grade constant received above, we fond that there might have been 262 animals in the second sample. Of course, this process of multiplication may be done by species too, thereby receiving values approximating the true individual numbers per species. It may be drawn as a moral that manual selecting, though made very thoroughly on a material brought home into the laboratory, is of a strikingly low grade of efficacy. By a hand-made sorting method, more than half of all the individuals present will remain behind in the sample, while even the simplest floating method will extract more than three-fourth of the individuals. Though I never controlled by this calculation the nemit floating method, its grade of efficacy, based on the data of Vágvölgyi, seems to be 83%. In view of the fact that his control may have been a manual selecting, which, as mentioned above, infers a certain amount of error due to its limited grade of efficacy even in the control, not even this 83% may really stand. It is well approached by the 77% of the fatty alcohol sulphonate method. In reality, the floating method has a somewhat better grade of efficacy than represented by the values above, because, in floating, some of the species remaining in the sample do not float for the very cause of their injured, broken or dirt-filled state, — and the float contains mainly the whole shells. There is no such difference in the case of a manual handling. Naturally, in special cases the grade of efficacy may also be specific ; certain mollusk species will hardly or not float at all, due to the special shape of their shells (Helicolimax, Daudebardia). For samples containing a greater amount of such species, — a rather rare occurrence — it were deserving to examine the grade of efficacy for these critical species, since it will be much dissimilar as related to the others. For that matter, I also investigated the grade of efficacy as a function of time involved in the process (the above example of the floating method) and I found that, in one of the samples, I received 108 specimens by manual selecting in 30 minutes, while, in the other sample, the floating process consumed 48 minutes of actual work, with its result of 246 shells. Of this latter, 152 specimens falls into 30 minutes, therefore floating, in a time function, is more productive by 28,9%. This much better result allows the reference that, in the case of mollusks, a manual selecting of the sifted samples is worth while (even from the point of view of simply collecting purposes) only if there is no possibility to take home the material for floating, as pointed out also by Vágvölgyi (Vágvölgyi 1952).
