We have compared two different laser-induced optical light traps for their utility in moving organelles within living animal cells and walled fungal cells. The first trap employed a continuous wave neodymium-yttrium aluminum garnet laser at a wavelength of 1.06 micron. A second trap was constructed using a titanium-sapphire laser tunable from 700 to 1000 nm. With the latter trap we were able to achieve much stronger traps with less laser power and without damage to either mitochondria or spindles. Chromosomes and (...) nuclei were easily displaced, nucleoli were separated and moved far away from interphase nuclei, and Woronin bodies were removed from septa. In comparison, these manipulations were not possible with the Nd-YAG laser-induced trap. The optical force trap induced by the tunable titanium-sapphire laser should find wide application in experimental cell biology because the wavelength can be selected for maximization of force production and minimization of energy absorption which leads to unwanted cell damage. (shrink)

This paper considers the relationship between G. H. von Wright's solution to the paradoxes of confirmation and his "Principal Theorem of Confirmation". The former utilizes the order of our knowledge of the qualities of confirming instances of an hypothesis; the latter states the way in which an instance contributes to the probability of an hypothesis. It is shown that these two, as stated by von Wright, are logically incompatible. Then the most thorough possible emendation of the paradoxes solution (...) is considered, and it is shown that this still prohibits use of the "Principal Theorem" to confirm hypotheses stating necessary causal conditions, and to confirm by deliberate experiment hypotheses stating sufficient causal conditions. It is concluded that any solution of the paradoxes must rest solely upon the relation of the data to the hypothesis involved. (shrink)